A two-stage method of producing phenol and ketone can involve continuously oxidizing an alkylbenzene with oxygen to form an intermediate, an alkylbenzene hydroperoxide. For example, oxidation of the alkylbenzene cumene, also referred to as isopropylbenzene, to produce the alkylbenzene hydroperoxide cumene hydroperoxide (CHP) is shown in reaction (I).

As shown in reaction (II), the intermediate CHP can then undergo acid decomposition with an acidic catalyst to form phenol and acetone. The mixture of phenol and acetone that is formed in the process can then be separated and purified such as by rectification on a distillation system.

The economic efficiency of the synthesis of phenol and ketone by the alkylbenzene oxidation method can depend on attaining the highest possible yield in the two stages process of alkylbenzene oxidation and alkylbenzene hydroperoxide decomposition (also referred to as the cleavage stage). Another factor in the production of phenol and ketone by this method can be the safety of production, since both reactions, i.e., the oxidation of alkylbenzene and the decomposition of alkylbenzene hydroperoxide, are exothermic. Moreover, alkylbenzene hydroperoxides, like many other peroxide compounds, can be thermally unstable. So close monitoring of the reaction conditions and the current concentration of alkylbenzene hydroperoxide in the reaction mixture can be important to ensure the necessary level of production safety.
The oxidation of alkylbenzene can be performed in a series of reactor vessels. The yield of alkylbenzene hydroperoxide obtained during this continuous oxidation process is a function of the steady-state concentration maintained in each of the reaction vessels. To obtain a high yield of alkylbenzene hydroperoxide and provide safe working conditions, samples of the reaction mixture are routinely taken from the alkylbenzene oxidation reaction vessels. The samples can be hand-carried to the laboratory and analyzed for their alkylbenzene hydroperoxide concentration by titration methods, which can ensure the greatest accuracy and reliability. The same method of manual sampling and titration in the analytic laboratory can be used for determining the residual concentration of alkylbenzene hydroperoxide after the initial stage of its acid decomposition. Since the stage of continuous decomposition of alkylbenzene hydroperoxide can be dangerous, laboratory analyses are generally done around the clock with a frequency of about 6 to about 12 times per day, or about every 2 to about 4 hours.
Analytical laboratory methods of determining the alkylbenzene hydroperoxide content under industrial production conditions can include iodometric titration and a wet photometric method, which involves measuring the optical density after an additional reagent is added to the solution containing alkylbenzene hydroperoxide. However, both of these methods can be rather complex, can rely on the use of expensive reagents, and can be impractical for continuous industrial processes.
Another method for monitoring the alkylbenzene hydroperoxide content can include using an “on-line” industrial calorimeter analyzer. However, this method is destructive and “infers” the concentration of alkylbenzene. In this method, heat is liberated and the corresponding temperature rise is recorded. The alkylbenzene hydroperoxide concentration is then calculated from the magnitude of the temperature rise. This method can be undesirable for commercial use, since it can require a complex apparatus, can use a complex scheme of streams, and can rely on precise metering to obtain reproducible results, and can be prone to fouling of the equipment. In addition, this method can be applicable only for low concentrations of alkylbenzene hydroperoxide. Moreover, this method is not applicable for measurements in the stream at the alkylbenzene oxidation stage.
Accordingly there still remains a need in the art for a direct, non-destructive, automatic, and real time measurement process for alkylbenzene hydroperoxide concentration in industrial streams that can be used to control the manufacturing process, such as allowing for closed loop control, and in a way that can reduce the reliance on cleavage process control reagents and can optimize the production of phenol and ketone using the alkylbenzene oxidation and decomposition method.